We have used a retroviral infection vector to modulate the levels of the MMP-inhibitor TIMP-2 produced by human melanoma A2058 cells. Altering the production of TIMP-2 modulates not only proteolysis of the extracellular matrix, but also the adhesive and spreading properties of the cells, motility of cells on and through matrix components, and invasion of reconstituted extracellular matrices. Altering the production of TIMP-2 also results in changes in cell morphology and in vivo tumorigenicity. These effects of TIMP-2 appear to be mediated by inhibition of gelatinase A activity. We conclude that gelatinase A, in addition to contributing to proteolysis of ECM components, also functions to proteolyze cell surface components that mediate attachment of A2058 cells to the ECM. Thus, gelatinase A may function to modulate cell attachment and facilitate cell migration and invasion. We have initiated the characterization of the cell-surface associated/adhesion promoting protein(s) that is(are) proteolyzed by gelatinase A and have identified a 45 kDa protein that increases over time upon incubation of A2058 cells with gelatinase A. Other less prominent bands were also evident. These proteins are undergoing N- terminal sequence analysis using Edman degradation. The relevance of these proteins to adhesion and degradation by gelatinase A will be studied.